Hymenoptera

Honey Bees, Wasps, Hornets, and Yellow Jackets

There are many venomous hymenopterans (eg, honey bees, wasps, hornet, yellow jackets), in which the female drone possesses a barbed ovipositor on the tip of the abdomen that connects to paired venom glands. Bees possess a barbed stinging apparatus; after stinging the victim, bees die because the stinger and its associated venom sac are pulled out of the abdomen. Wasps, hornets, and yellow jackets possess a stinging apparatus that is not barbed; they are capable of stinging multiple times. The venom glands of honeybees contain a hydrolyzing protein, mast cell degranulating peptides, a phospholipase, hyaluronidase, vasoactive amines, and a neurotoxin apamin.

A single bee sting will produce pain, swelling, erythema, edema, and local induration, which can be followed by pruritus at the injection site. The incidence of anaphylactic reactions is not known in companion animals—if a severe systemic reaction has not occurred within 30 min, it is not likely to occur. In dogs, bee and wasp stings cause only local redness, erythema, and transient pain. Dogs may vocalize when stung and may rub their mouth and eyes on the ground. Usually cutaneous reactions appear quickly and regress spontaneously. With repeated stings, anaphylaxis, with salivation, vomiting, diarrhea, circulatory collapse, pallor, or cyanosis, may result (see Excessive Adaptive Responses).

The stinger/ovipositor (if present) with accompanying venom glands should be removed, if it can be located. In severe cases with urticaria, epinephrine should be given IM. In cases of anaphylaxis, epinephrine should be immediately administered, SC, at a dosage of 1:1,000 (0.1–0.5 mL) for dogs or cats. This dosage can be repeated every 10–20 min. When given IV, it must be diluted to 1:10,000, and 0.5–1.0 mL is administered with vigilant monitoring of heart rate, heart rhythm, and blood pressure. IV fluids are indicated to prevent vascular collapse. Antihistamines and corticosteroids should also be given. The animal may require intubation to provide supplemental oxygen.

Africanized Honeybees (“Killer Bees”)

The common honeybees in America were brought to the New World by European settlers; as a result, the European varieties of honeybees established themselves throughout North and South America. In the 1950s, African colonies of bees were crossed with the docile European varieties of honeybees in laboratories in Brazil, but their offspring managed to escape from the laboratory environment. These hybridized offspring were characterized by excitability, aggressive defense of the hive, and frequent swarming activity. Since their escape in 1957, these “killer bees” have spread throughout most of South America, through Central America and Mexico, and into the southern regions of the USA; their range is expected to expand northward.

Africanized bees are difficult to distinguish morphologically from their European counterparts. Their stinging behavior is primarily defensive, eg, in response to a perceived threat to the colony. These bees habitually sting en masse. Once initiated, stinging recruitment within the colony can result in hundreds or thousands of stings; bees may pursue their victim for as far as 1 km. Hives are generally found in exposed locations such as on tree branches or in old tires or boxes where domesticated animals may come in contact with them. Stings occur generally in the vicinity of the hive. Smaller pets are particularly susceptible to the effects of multiple stings, because they receive a larger dose of venom/kg body wt. It is the cumulative dose of venom that becomes fatal.

Animals that receive massive envenomations are visibly depressed and usually febrile. They may exhibit facial paralysis, ataxia, seizures, and neurologic signs. The urine may be dark brown or red, and the feces are bloody. Bloody or dark brown vomitus may be seen. Leukocytosis may be present. The animal may be thrombocytopenic; disseminated intravascular coagulation may be imminent. Urinalysis may reveal granular casts due to renal tubular damage. The animal may develop acute renal failure caused by acute tubular necrosis or direct toxic effect of massive envenomation. Dogs may develop a secondary immune-mediated hemolytic anemia.

Access to cardiac monitoring, supplemental oxygen, "crash cart" drugs, and airway intubation must be readily available. Any animal that receives massive, multiple stings must be hospitalized, treated aggressively, and hospitalized for 24 hr after cessation of clinical signs.

Fire Ants

Fire ants (red imported fire ants and black imported fire ants) are not native to North America but were introduced into the USA in the early years of the 20th century. Since their introduction, red imported fire ants (Solenopsis invicta) have colonized more than 310 million acres in 12 southern states, whereas black imported fire ants (S richteri) have been contained in a small area in Alabama and Mississippi. Fire ants attack domestic animals and native wildlife. The ant anchors onto its victim with its prominent mandibles, tucks its abdomen under its body, and stings with its nonbarbed stinger, a modified ovipositor with an associated venom gland. It retracts its stinger, rotates its body to the side, and stings again. This act is repeated in a circular pattern. Unlike bees, wasps, and hornets, fire ants inject their venom slowly. Each ant can deliver 0.11 μL with a total of 20 consecutive stings before the venom gland is depleted.

The typical reaction to a fire ant sting is a wheal and flare, which usually resolves within an hour. Pain and inflammation begin immediately. A papule will form at the sting site and develop into a sterile pustule. These pustules are pruritic and may become secondarily infected due to self-inflicted trauma. Regional reactions can occur and may be erythematous, indurated, and quite pruritic. Regional edema may be severe enough to impede blood flow to a limb. Systemic or anaphylactic reactions can produce clinical signs removed from the site of the initial sting, including urticaria, cutaneous edema, laryngeal edema, bronchospasm, vascular collapse, and death. Deaths due to systemic anaphylaxis occur within minutes of the sting, whereas deaths due to venom toxicity occur >24 hr after the sting.

There are no treatments to prevent or resolve localized reactions to fire ant stings; however, symptomatic therapy might be beneficial. Local reactions may be treated with antihistamines, topical corticosteroids, water or alcohol compresses, ice, and topical treatment with menthol and camphor. Warm baths may provide some relief for dogs. Regional reactions occur less frequently and should be treated with antihistamines, corticosteroids, analgesics, and fluid therapy. Antibiotics are indicated for secondary infections. Anaphylactic reactions to fire ant stings are treated similarly to those from honeybees, wasps, and, yellow jackets (see Honey Bees, Wasps, Hornets, and Yellow Jackets).